Mass spectrometry using a quadrupole ion filter, also referred to as quadrupole mass spectrometry, has been used for many years. Mass spectrometry using a quadrupole ion filter, referred to as a “quadrupole” uses four parallel rods that are supplied with a direct current (DC) voltage and a superimposed radio frequency (RF) voltage. The DC and RF voltages enable the quadrupole to scan a mass range by scanning over a range of preselected radio frequencies.
Typically, when scanning a mass range using the quadrupole to locate ions having a particular mass, the DC and RF voltages are maintained in a constant proportion to each other and are adjusted over a time period to filter ions having different mass. To scan a mass range, the DC and RF voltages are adjusted in steps that correspond to the atomic mass of the ions sought to be filtered. For example, the DC and RF voltages are adjusted to identify ions in, for example, 0.1 atomic mass unit (AMU) steps. Adjusting the DC and RF voltages over a mass range allows the mass spectrometer to identify different ions and associated isotopes according to the mass of the ion and isotope. Each step in DC and RF voltage, corresponding to the AMU step, requires the electrical circuitry that generates the respective DC and RF voltages to stabilize prior to analyzing (referred to as integrating) the results provided by the quadrupole and related detector. Unfortunately, for a given AMU step size, as the speed at which it is desirable to scan the quadrupole continues to increase, the amount of time available for analyzing the signal decreases.
Accordingly, a need exists for a way of maximizing the detection capability of a quadrupole as scan speed increases.